Zyxel NSA325 messed up uboot - recovery - de-brick (no replies)

@brodhi

i have a 2nd nsa325 which i fu**ed up some years ago while flashing uboot (maybe corrupt).
now i tried to kwboot it but it works only parcially:

Zyxel-NAS325-OpenWRT$ kwboot -t -B 115200 /dev/ttyUSB0 -b uboot.2025.10-tld-1.nsa325.kwb -p
kwboot version 2025.01
Detected kwbimage v0 with NAND boot signature
Patching image boot signature to UART
Sending boot message. Please reboot the target...|
Sending boot image header (512 bytes)...
 25 % [....                                                                  ]
Done
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Done
Finishing transfer
[Type Ctrl-\ + c to quit]

and thats it. i tryed several uboots which is know are working (tested on the 2nd box).

i also read: https://forum.doozan.com/read.php?4,140145,140214

any tips what to do?